This invention is concerned generally with testing of microprocessor systems, and more particularly, with a device for controlling and monitoring the microprocessor in the system.
With the rapidly escalating use of microprocessors in electronic systems of all kinds, the testing and debugging of such systems has become a major concern. In the prior art, it is known to use "signature analysis" at various points in the system. This can be accomplished with a device such as the Model 5004A by Hewlett-Packard Company, which compares a known "good" bit stream against the empirical bit stream measured at selected test points in the system. Although some information is obtained through the signature analysis, detailed information about the system operation is not revealed.
The use of logic state analyzers such as the Model 1661A by Hewlett-Packard Company provides more information about the system under test. These analyzers provide passive monitoring of the hardware and measurement of logic levels on the system data bus, address bus and control bus lines. Although information about the system is received, control of the system is not obtained through such devices.
The deficiency of logic state analyzers related to control has been remedied by the use of in-circuit emulators such as the ICE-80 (8080 in-circuit emulator) from Intel Corporation, which are microprocessor based test systems which perform exactly like the microprocessor component system under test. Generally, the emulation of the microprocessor is accomplished on a small computer system, so that the user has some control over data entry and output into the system under test. However, detailed control of each microprocessor pin is still not possible.
In yet another level of sophistication of the in-circuit emulator, a "stand in" for the microprocessor has been developed which enables the user to single step through the normal sequencing of the microprocessor in the system under test. Even with the use of these stand in testers, it is still a problem with the testing of microprocessor systems in that control of the microprocessor is limited to the single "machine cycle." That is, the microprocessor can only be "frozen" or stopped in certain very specified electrical cases.